Process for the recovery of metals from sulfide ores through electrolytic dissociation of the sulfides

ABSTRACT

A POLLUTION-FREE PROCESS FOR THE ELECTROLYTIC DISSOCIATION OF SULFIDE ORES OF THE METALS OF GROUPS I-B, II-B, IV-A, V-A, VI-A AND VIII OF THE PERIODIC TABLE IN AQUEOUS ACIDIC MEDIA WITH THE FORMATION OF METAL IONS AND ELEMENTAL SULFUR FOLLOWED BY RECOVERY OF THE METAL IONS FROM SOLUTION IN THE ELECTROLYTE MEDIA, THE PROCESS CHARACTERIZED BY CERTAIN PROCESS CONDITIONS, THESE BEING THE USE OF: (1) AN ELECTROLYTE COMPRISING A SOLUBLE METAL CHLORIDE SELECTED FROM THE GROUP CONSISTING OF SOLUBLE CHLORIDES OF ALUMINUM, CHROMIUM, COPPER, IRON, MANGANESE, NICKEL, ZINC AND RARE EARTH METALS ALONE OR MIXED OR IN COMBINATION WITH ALKALI METAL AND/OR ALKALINE EARTH METAL CHLORIDES, THE ELECTROLYTE BEING AT LEAST .5 MORMAL IN CHLORIDE ION, (2) A SULFIDE FEED OF AVERAGE PARTICLES SIZE SMALLER THAN ABOUT 60 MESH U.S. STANDARD, (3) A PH RANGE OF UP TO ABOUT 3.9, 74) AN ELECTROLYTE TEMPERATURE RANGE BETWEEN ABOUT 50*C.-105*C., AND (5) AN ANODE CURRENT DENSITY ABOVE ABOUT 12 AMPERE/ FT.2.

United States Patent US. Cl. 204-105 R 37 Claims ABSTRACT OF THEDISCLOSURE A pollution-free process for the electrolytic dissociation ofsulfide ores of the metals of Groups I-B, II-B, IVA, V-A, VI-A and VIIIof the Periodic Table in aqueous acidic media with the formation ofmetal ions and elemental sulfur followed by recovery of the metal ionsfrom solution in the electrolyte media, the process characterized bycertain process conditions, these being the use of:

(1) An electrolyte comprising a soluble metal chloride selected from thegroup consisting of soluble chlorides of aluminum, chromium, copper,iron, manganese, nickel, zinc and rare earth metals alone or mixed or incombina tion with alkali metal and/or alkaline earth metal chlorides,the electrolyte being at least .5 normal in chloride (2) A sulfide feedof average particle size smaller than about 60 mesh US. Standard,

(3) A pH range of up to about 3.9,

(4) An electrolyte temperature range between about 50 C.-l05 C., and

(5) An anode current density above about 12 ampere/ ft.

BACKGROUND OF THE INVENTION There are disclosures in the prior art ofprocesses for the electrolytic recovery of certain metals from theirsulfide ores under various conditions. These processes cannot be usedfor the economic recovery of metals of Groups I-B, II-B, IV-A, V-A, VI-Aand VIII of the Periodic Table from their sulfide and mixed sulfideores, particularly low grade ores, for various reasons.

U.S. Pat. No. 2,839,461 discloses an electrolytic process for therecovery of nickel from nickel sulfide but it is dependent upon theformation of a highly conductive nickel sulfide matte anode and is notapplicable to low grade concentrates. Such common sulfide minerals asgalena, sphalerite, chalcopyrite, and chalcocite have resistivities manytimes that of the anode used in the processes of Pat. No. 2,839,461 and,therefore, that process cannot be used with these minerals.

US. Pat. No. 3,464,904 relating to the electrolytic recovery of copperand zinc from their sulfide ores discloses the use of a hydrochloricacid electrolyte having a concentration of 510%. In the absence of themetal chlorides used in the electrolytes of co-pending application Ser.No. 113,751 and in the electrolytes of this application, this highacidity does not lead to economic recovery from their sulfides of themetals to which the present invention applies as demonstrated in Example8 which follows.

Prior to the present time there has been little incentive for thedevelopment to commercial application of electrolytic or otherpollution-free processes for the recovery of metals from sulfide ores.Metals are conventionally recovered from their sulfide ores bypyrometallurgical processes in which sulfur contained in the ores orconcentrates is oxidized to sulfur dioxide, of which a substantialportion is released to the atmosphere with consequent damage to theenvironment and loss of sulfur values. Recently promulgated pollutionstandards have made the pyrometallurgical processes, as presentlyapplied, prohibitive 3,736,238 Patented May 29, 1973 and have createddemands for pollution-free processes. An electrolytic process requiringonly economic quantities of power, in which substantially all the sulfurin the above metal sulfides related to this invention is converted toelemental sulfur is an answer to the pollution problem.

The high degree of concentration required for economic pyrometallurgicalprocessing results in losses in concentration and in the loss ofpotentially valuable co-product values which are not readily recovered.The presence of coproduct values in the main metal product often resultsin economic penalties being assessed against the concentrates. Thus lowgrade concentrates which are not amenable to physical segregationtechniques are often considered valueless or of low value because theycannot be processed economically by conventional pyrometallurgicalprocesses.

In co-pending application of Ser. No. 113,751, filed Feb. 8, 1971, byPaul R. Kruesi, now U.S. Pat. No. 3,673,- 061, it is disclosed that theuse of a basic electrolyte media for electrolytic dissociation ofsulfide ores results in the sulfide sulfur being converted into sulfatewith high current consumption while the use of an acidic electrolytemedia comprised of alkali metal and/or alkaline earth metal chloridesunder specified conditions results in the sulfide sulfur being convertedto elemental sulfur with a substantial reduction in required current.

While the use of alkali and alkaline earth metal chlorides aselectrolytes as disclosed in the above cited application Ser. No.113,751 results in an economic pollutionfree process for the processingof sulfide ores and concentrates, it has been found that certain othermetal chlorides under the conditions herein specified are equallyeffective as electrolytes for the same purpose and in certain cases haveunexpected advantages.

Many commercial sulfide concentrates contain substantial quantities ofiron either as a part of the mineral as in the case of chalcopyrite ormarmatite, or as an impurity as is the case with pyrrhotite. In theprocess of this invention the conversion of this iron to chlorideresults in a convenient electrolyte media.

In the past it has been difficult to process galena in a chloride mediabecause of the limited solubility of lead chloride. Particularly, it wasgenerally believed that this low solubility would mitigate againsteconomic plating at the cathode. It has been found that the solubilityof lead chloride is surprisingly high in aluminum chloride and thataluminum chloride is a suitable electrolyte media for the efficientelectrolytic dissociation of lead sulfide and subsequently plating oflead at the cathode. This is clearly shown in Example 6 below.

STATEMENT OF THE INVENTION The term metal sulfide as used herein isinclusive of the complex as well as the simple sulfide minerals whichcontain economically recoverable quantities of the specified metals.

The invention is a pollution-free process for the recovery of the metalsof Groups IB, IIB, IVA, V-A, VI-A and VIII of the Periodic Table, fromtheir sulfide and mixed sulfide ores or concentrates in which thesulfide is electrolytically dissociated in an acid aqueous media intoelemental sulfur and metal ions which are then recovered from solutionin the electrolyte media by conventional pollution-free techniques.

The electrolysis process is characterized by certain critical processconditions which render it economically feasible, these being the useof:

(1) An electrolyte comprising: a soluble metal chloride selected fromthe group consisting of soluble chlorides of aluminum, chromium, copper,iron, manganese, nickel, zinc and rare earth metal chlorides eitheralone or mixed in combination with alkali metal and/or alkaline earthmetal chlorides, said electrolyte being at least .5 normal in chlorideion,

(2) A sulfide feed of average particle size smaller than about 60 meshUS. Standard,

(3) A pH range up to about 3.9,

(4) An electrolyte temperature range between about 50 C.-105 C., and

(5) An anode current density of above about 12 amperes/ftfi. Thetemperature and pH ranges are the most critical of the above parameters.Within the above process parameters the chloride electrolytes of thisinvention are substantial equivalents for electrolytic dissociation ofthe metal sulfides of metals of Groups I-B, II-B, IVA, V-A, VI-A andVIII of the Periodic Table.

The other soluble halide salts, including the bromides, iodides andfluorides, of aluminum, chromium, copper, iron, manganese, nickel, zinc,and rare earth metals, are operative for the purpose of the invention;however, they are not as economically attractive as the chlorides ofthese metals. Soluble halide metal salts in general are operative aselectrolytes for recovering metals from their sulfides in accordancewith the process of the invention.

DETAILED DESCRIPTION OF THE INVENTION The economic feasibility of theprocess is dependent upon the current required to produce a givenquantity of metal. It is expressed herein as the ampere hours of currentrequired to release a pound of metal. The current requirement will varyfor each metal and economic viability will depend somewhat on the costper pound at which that metal can be produced by present processes. Thisstatement does not take into consideration recently promulgated airpollution standards which may completely eliminate or drastically limitthe economic competition of present air polluting processes.

The process parameters which have been found to control the currentrequirements for the process are electrolyte composition, feed particlesize, operating pH range, operation temperature, and anode currentdensity. As the examples which follow show, these factors are mutuallyinteracting and dependent as respects their effect on cur rentrequirements.

It has been found that sulfide ores and concentrates of metals of GroupsI-B, II-B, IV-A, V-A, VIA and VIII of the Periodic Table arecharacterized by certain similar properties related to the electrolyticdissociation to elemental sulfur and metal ions therefrom by the processof this invention. For example, their sulfides all have relatively lowconductivities. While certain nickel sulfides are relatively goodconductors, others are not. Further, the metal ions of these sulfidesare most favorably produced by electrolysis in aqueous acidicelectrolytes of soluble chlorides of aluminum, chromium, copper, iron,manganese, nickel, zinc, rare earth metals, alkali metals, and alkalineearth metals, and mixtures thereof, at a pH range of up to about 3.9using anode current densities above about 12 amperes/ft. with a sulfidefeed particle size smaller than about 60 mesh US. Standard, and atemperature range between about 60 C.-l05 C. for the alkali and alkalineearth metal chlorides and between about 50 C.-l05 C. for the otherelectrolytes. The examples which follow illustrate that the powerrequirements for the process applied to recover the stated metals fromtheir sulfides are well within the limits of commercial feasibility.

The minerals containing the metals which can be recovered by the processoften contain the metals in the form of complex or mixed sulfides.

The electrolytic media for the process must be acidic as an alkalineelectrolyte has proven unsatisfactory for recovery from their sulfidesof the defined metals to which the invention is related. Elementalsulfur is not stable in an alkaline media because oxidation of thesulfur proceeds rapidly through thiosulfate, hydrosulfite, sulfide tosulfate. The presence of sulfate ions is undesirable because at highsulfate concentrations oxygen is rapidly evolved at the anode resultingin a decrease in current 4 efiiciency. Further, it was found that athigh current densities in the presence of sulfate graphite anodes Wereappreciably attacked and this type anode is the most satisfactory.

The preferred electrolyte media has been set forth above. Ferrouschloride is particularly effective as an electrolyte for dissociation ofchalcopyrite as this compound is produced in quantity by theelectrolytic dissociation of chalcopyrite in an acid medium. Aluminumchloride is particularly suited as an electrolyte for the dissociationof lead sulfide ores and concentrates, leadzinc and lead-silverconcentrates, because of the high solubilities of lead and silverchloride in aluminum chloride. This discovery is highly unexpected inview of the insolubility of lead and silver chlorides in most solvents.Zinc chloride is preferred with zinc ores essentially free of lead.

Concentrations of chloride ion in excess of .5 normal to saturation maybe used for the process. Voltage across the cell is lower at higher saltconcentrations and the latter are preferred except Where low grade feedsare used and where salt losses would therefore become significant.

It is highly important that a high percentage of the sulfur in the metalsulfide be recovered as elemental sulfur both from the standpoint ofpollution control and the electrical efiiciency of the process. Ifsulfur is converted to sulfate, high current consumption results and thedisposal of the sulfate may create a pollution problem. Every mole ofsulfur which is oxidized beyond the elemental state requires sixFaradays which is equivalent to 2275 ampere hours per pound of sulfur.As chalcopyrite, for example, contains approximately one pound of sulfurper pound of copper, any sulfur oxidation of the sulfate represents asubstantial loss of efiiciency. As shown by the examples below, anaverage of at least 90% of the sulfur in the sulfides is converted toelemental sulfur in the process of the invention. The elemental sulfurdoes not result in any polarization problems at the reactiontemperatures of the electrolyte media.

The particle size of the feed material is critical as it directlyaffects the conversion of sulfide sulfur to elemental sulfur. Theelemental sulfur produced is extremely fine. The anode current attacksthe metal sulfide preferentially to sulfur provided the sulfide hassutficient activity near the anode. The activity of the sulfide is afunction of its concentration and its exposed surface area. Therefore,the presence of a high concentration of fine sulfide near the anodeprevents the continuing oxidation of sulfur and results in higherefficiency and conseqeuntly lower current consumption. An average grainsize for the feed sulfide smaller than about 60 mesh U.S. Standard isthe operable range and is compatible with other critical parameters.

A pH range for the electrolytic media up to about 3.9 is preferred.Current efiiciency is reduced at pHs above 3.9 and at very highacidities (low pH values) in the absence of substantial concentrationsof the specified metal chlorides. In certain cases such as that ofaluminum chloride which hydrolyzes at about pH 2.0, chromic chloridewhich hydrolyzes at about pH 3.0, and rare earth metal chlorides whichhydrolyze at about pH 4.0, the acidity must be strong enough to preventthis hydiolysis. The preferred pH range is 0.3-0.8. The pH of theelectrolyte is conveniently adjusted with hydrochloric acid.

The reaction temperature of the electrolyte is critical and high processefficiency is not obtainable at low temperature. The preferential attackon the sulfide over elemental sulfur is accentuated at high temperaturesand, indeed, at temperatures below 50 C. a substantial portion of thesulfide is converted to undesirable sulfate. The operable range is about50 C.l05 C. when used in conjunction with the other critical factors. Atemperature of C. is most preferred.

The anode current density is also critical as used with the othercritical parameters with a preferred range being above about 12amperes/ft. anode current density. In contrast to the earlier prior artteaching (U.S. Pat. No. 2,761,829) it was found that high copperdissociation in copper sulfide concentrate in the presence of ironsulfide (pyrite) was attained at current densities of 240 .amperes/ft.For the mixture of chalcopyrite and pyrite where chalocpyrite is thepredominant mineral, a preferred current density range is 120-240amperes/ft. Where pyrite predominates current densities of between60-120 'amperes/ft? are preferred.

Within a fairly broad range current anode density may 6 in the processof the invention as operated within the critical parameter ranges oftemperature, current density, pH and particle size.

For each test 400 grams of comemrcial copper sulfide concentrate havinga particle size of 60 mesh analyzing by weight 27.7% copper and 28.4%iron was slurried in 2 liters of electrolyte and subjected to 30amps/hr. of current under the conditions shown. For the mixedelectrolytes approximately equal volumes of each were used. Other alkalimetal chlorides may be added to the electrolyte, such as, potassium andlithium chlorides. Alkaline earth metal chlorides, such as, calcium andbarium chlorides may be added.

Test No 1 2 3 4 5 6 Electrolyte 2 M A1013..." 1 M A1013... 2 M NaCl; 0.5M FeOlz--- 2 M NaCl; 3 M FeCli.

1 M A1013. 1 M FeClz. Temperature 0.)- 78 74 75 75 75 75. Anode currentdensity (ACD) (amps/ft!) 1 120 120 12 120 120. pH-.. 0.4-. 0.5.... 0.6.-0.6- 0.5.. 0.6. Amp-hrsJlb. Cu recovered 488 561 581 613 654 558,Percent S as elemental S. 93 88---" 90 88 87 88.

be adjusted to the situation so long as it is above about 12 amperes/ft.With low grade feeds an anode current density between 40-120 amperes/ft.may be used. Often when metal is being plated at the cathode thenecessities of cell geometry will dictate the anode current density.Thus with copper if copper powder is desired current densities of100-200 amperes/ft. are preferred at the cathode and this range ofcurrent density is suitable for high grade copper concentrates. Whenplating lead or zinc at the cathode a current density range of 20-30amperes/ft. is preferred at the cathode and is suitable for the anode.

The following examples with results are illustrative of the process ofthe invention but not limiting thereof. The process is not limited to aspecific electrolytic cell design or type of cell. The cells used in theexamples, well known in the art, comprised an anode section containing asuitable anode such as graphite or coated titanium, provided with meansfor agitation and heating, and separated from the cathode section by adiaphragm. The cathode section consisted of a suitable cathode ofstainless steel, copper, lead or aluminum depending upon the metal beingplated or the cathode reaction desired and was provided with means forliquid circulation and heating.

In the examples, average grain size is given in U.S. Standard mesh size,anode current density designated as The high conversion of sulfidesulfur to elemental sulfur and low current consumption prove theeffectiveness of the electrolytes within the parameter ranges of theprocess. As in the examples which follow in which it is reported thehigh conversion of sulfide sulfur to elemental sulfur in the acidelectrolyte and low current consumption is in marked contrast to priorart processes using basic electrolytes resulting in conversion of thesulfide sulfur to sulfates with consequent high current consumption.

l EXAMPLE 2 Selection of the following tests was made to demonstrate theequivalence for the purposes of the invention of the electrolytes ofExample 1 and the electrolytes nickelous chloride, cupric chloride,chromic chloride, managanous chloride, and rare earth metal chlorides.

For each test 400 grams of mesh particle size copper sulfide concentrateanalyzing by weight 27.7% copper and 28.4% iron were slurried in 2liters of electrolyte and subjected to 30 ampere hours of current underthe conditions shown. Analysis by weight of the rare earth metalchloride mixture as oxides was as follows: La O -78.7%, Ce O -l1.2%,PI203'3.8%, Nd2031%, Sm203-2%.

Test No 1 2 3 4 5 Electrolyte 1 M NiClz 1 M 011012 1 M CrCla 1 M M110121 M (rare earth) (31 Temperature 0.)- 74 7 75-.. 75 75. ACD (amps/ft?)120 120 120. 120 120, pH-- 0.6 0.5- 0.5. 0.5- 0.5. Amp-hrsJlb Curecovered-- 586 745 799.. 601 565 Percent S as elemental S. 87 85 94 85.

ACD is given in amperes/ft. current requirement is 55 The results of theexample in terms of large conversion reported in terms of ampere hours/pound of metal dissociated, and recovered. The percent sulfur convertedto elemental sulfur is computed by dividing the amount converted toelemental sulfur by the total amount of sulfur converted from sulfidesulfur and is expressed in percent.

The metal dissolved in the electrolyte can be finally recovered byconventional methods such as, electrolysis, precipitation, cementation,etc., depending on the metal being recovered. In certain cases the metalcan be plated out on the cathode during the dissociation process andrecovered in this manner.

Elemental sulfur is readily recovered from the electrolyte media by theprocess disclosed in co-pending application Ser. No. 233,352, filed inthe U.S. Patent Office on Mar. 9, 1972, William G. Kazel, entitledSulfur Recovery Process.

EXAMPLE 1 The following tests were selected to illustrate theoperativeness of aluminum chloride and ferrous chloride alone and withan alkali metal chloride as electrolytes of sulfide sulfur to elementalsulfur with low current consumption demonstrates the effectiveness ofthe electrolytes under the conditions for a representative metalsulfide. In the case of all the electrolytes used in the tests exceptcupric chloride and chromic chloride the copper was recoveredessentially as cuprous copper resulting in very high electricalefliciency. The copper recovered using cupric chloride and chromicchloride electrolytes was essentially cupric copper, this accounting forthe somewhat higher current consumptions. The higher valent forms ofcopper and chromium are preferred because the lower valent forms havelimited solubility. However, cuprous chloride may be used as theelectrolyte instead of cupric chloride.

EXAMPLE 3 In order to define the critical temperature range for theprocess utilizing other conditions within the process parameter rangesthe following tests were performed.

For each test 400 grams of 60 mesh particle size commercial coppersulfide concentrate analyzing by weight 27.7% copper and 28.49% ironwere slurried in 2 liters lyte were separated to enhance plating of leadand zinc of of electrolyte and subjected to 30 ampere hours of currenthigh purity. The electrolyte media was sub ected to 38.3 under theconditions recorded. ampere hours of current before analysis for resultsat an Test No 2 3 4 5 6 2M AlCl 2 M A101 2 M A101 a u FeGl a M FeCl a Mneon.

''llllf" 7R 3 so a 44 .1 75 -5 so .f so. AIgD (amps/it.- (1)22.--"imp-braille. 3n recovered 488:- Percent S as elemental S 93..-

The results show striking increase in current consumpanolyte pH of 0.5,a temperature of 80 C., and a curtion and decrease in conversion ofsulfide sulfur to ele- 1 mental sulfur at temperatures below about 50 C.with current consumption as high as 2193 amp/lb. Cu rerent density of 30amps/ft. on both the anode and cathode. The following results wereobtained.

covered and sulfur conversion as low as 54%. The r sults t l Lead ZineIron Silver illustrate that the lower limit o the Critical temperatureDissolved metal (gms.) 76.0 33.8 10.3 .044 range is somewhere betweenabout 44-50 C. Percentage r v y of metals 97.7 27.3 31.9 69.8 EXAMPLE 4133 grams of lead were plated at the cathode indicating The followingtests are incuded to demonstrate the 0p- 90% cathode current efficiency.erativeness of the process at high acidities. The electrolysis wascontinued for an additional 65.6 For each test 400 grams of 60 meshcommercial ampere hours with the same anolyte pH and temperature coppersulfide concentrate assaying by weight 27.7% copusing anode and cathodecurrent densities of -60 amps/ per and 28.4% iron were slurried in 2liters of electrolyte ft. Zinc chloride dissolved in aluminum chloridewas and subjected to 30 ampere hours of current under the used as thecatholyte. The following results were obconditions indicated with thefollowing results. tamed.

Test No no--. 1 2 3 4 5 6 7 Electrolyte 3 M Fe C12. Temperature C 75.ACD (amps/m 120-" 1 0. 0 120-.. 120. pH 0.01 (5%HC1)- 0.4 1.0 2.0.-.0.01 (5%}101 l.4 2. lAmp-hrsJlb. Cu recovered 463 483 9 488 582-.- 6,486Percent S as elemental S 95.- 3 93 0 88 92.

The results demonstrate the effectiveness of the process at acidities ashigh as pH 0.01. The economically feasible Metal Lead Zinc Iron Silvermaximum PH is about llgissolvted metal (gmsf) E 1 77, 5 93 4 17 1 05gEXAMPLE 5 ercen g l ve y 0 me a s 99. 6 79.5 52, s 93.

The following test is included to show the eifectiveness 70 grams ofzinc were plated at the cathode indicating of the process utilizing arepresentative electrolyte on the a cathode current efficiency of 91%.sulfides of nickel and cobalt. The example illustrates that lead, zinc,and silver can For each test 400 grams of a 60 mesh particle size berecovered from their sulfides by the process of the low grade sulfideore concentrate assaying by weight invention using a representativechloride electrolyte for 8.33% nickel, 0.337% colbalt, 5.16% copper and37.8% the process of this invention and that the process is pariron wereslurried in 2 liters of electrolyte and subjected ticularly effectivefor these metals with an aluminum to 60 amp'ere hours of current underthe conditions shown. chloride electrolyte.

Using a 4 M FeCl electrolyte at a temperature of 80 The process isequally effective for the recovery of gold, C., pH of 0.5 and an anodecurrent density of 120 amps/ germanium and tin from their sulfides. ft.the following results were obtained from analysis of the electrolytemedia at the end of the test. EXAMPLE 7 The following test is includedto show the suitability of Wt. of metal dissolved (gins) Fe-46 Ni1.7Co-0.2 Oil-2.0 ferrous chloride electrolyte for recovering lead, zinc,Gum Sulfur recovered 5 ilv r n Cadmium from their sulfides.

Amp-hrsJlb. of combined 470 grams of mesh particle size sulfide oreconmetals recovered 5425 centrate assaying by weight 31 9% zinc 17 1%lead 5 l tal s 9s Percent age men 12.6% lI'Ol'l, .02 19% silver, and.018% cadmium were The low current consumption and high Sulfur converslurried in liters of electrolyte and fed to the anode sion obtainedillustrate the effectiveness of the process for slde f 3 dla'phrajgmcell- The 2 molar ferrous the recovery of nickel and cobalt from theirsulfides chloride, was sub ected to 157.5 ampere hours of current at 800, pH 0.5 at an anode current density of 60 amps/ EXAMPLE 5 ft. Theresults obtained are shown below.

The following example is included to show the effectiveness of theprocess for the recovery in chloride electrolyte Metal Pb Zn Ag Fe Cd ofadditional metals from their sulfides, particularly lead. l ussolv stlmetal (gmsf) 132.; 03 39. .07 500 grams of a -60 mesh particle sizecommercial sul- 7O iff age g 0 me a fide ore concentrate assaying byweight 25.6% lead, percht t iesfitii s13:I:::::::::::::::::::::::::::::::

24.8% zinc, and 013% silver were processed in a diaphragm cell. Theconcentrate was slurried in 2 liters of 2 The high percentage recoveryof lead, zinc, silver and M AlCl which served as anolyte. Lead chloridedissolved cadmium demonstrates the suitability of ferrous chloride in 2M AlCl served as catholyte. The anolyte and cathoas an electrolyte forrecovery of the metals from their sulfides by the process. Commerciallyfeasible current consumptions were noted.

EXAMPLE 8 Test N 1 2 3 Electrolyte HCl (5%) 2 M A1013.-- 3 M FeClz.

Temperature C.) 80

pH 0.01 (5% H01)- 0.01 (5% H01). 0%

ACD (amps/ft!) 12o 12o- 12 Amp-hrs/lb. Cu re- 1,566 463 558.

covered.

Percent S as elemental S. 73 r.' 95 88.

The results demonstrate the superiority of aluminum chloride and ferrouschloride acidified with hydrochloric acid over hydrochloric acid aloneas electrolytes.

EXAMPLE 9 Test No 1 2 Electrolyte 3 M FeClz 3 M FeClz. Temperature C.)-75 75. pH 0.5- 0.5. ACD (amps/ft?) 120 240. Amp-hrsJlb. Cu recovered 558617. Percent S as elemental S. 88 86.

The example shows that, somewhat contrary to the teaching of US. Pat.2,761,829; copper dissolves readily at the high current densities shownunder the process conditions of the invention.

EXAMPLE 10 The following tests were performed to demonstrate theeffectiveness of zinc chloride as an electrolyte.

For each test 400 grams of a -60 mesh grain size commercial zinc sulfideconcentrate assaying by weight 57.2%

10 EXAMPLE 11 The following tests were performed to determine theeffectiveness of the process of the invention in recovering arsenic,cadmium, antimony and selenium from their sulfides.

232 grams of a mesh grain size commercial low grade chalcopyriteconcentrate analyzing by weight 4.0% lead, 9.2% zinc, 24.0% pper, 25.5%iron, 0.5% arsenic, 0.018% cadmium, 0.025% antimony and 0.36% seleniumwere slurried in 2 liters of 3 M ferrous chloride electrolyte andsubjected to 30 ampere hours of current at 0., pH 1.5, and an anodecurrent density of 60 amps/ft. with the following results.

Percent metal Metal: dissolved Copper 9.4 Zinc 36.4 Lead 87.4 Arsenic97.0 Cadmium 42.9 Antimony 52.0 Selenium 28.9

As demonstrated with a representative electrolyte the process iseffective for the electrolyte recovery of the metals arsenic, cadmium,antimony and selenium from their sulfide ores. The process is equallyeffective for the recovery of bismuth and tellurium from their sulfides.

The current requirements set forth in the examples are well withincommercial feasibility ranges for large scale production of the metalsfrom their sulfide and mixed sulfide ores. The cost of the recovery ofthe metals from the electrolyte after electrolysis by conventionaltechniques is comparatively small. The process permits the recovery insignificant yields of metals present in trace quantities. The highpercentage recovery of sulfur from the sulfides as elemental sulfursubstantially reduces the pollution problems associated with prior artprocesses and enhances the economic attractiveness of the process.

Accordingly, the invention provides a process for recovery of the metalsfrom their sulfide and mixed sulfide ores which has the advantages ofbeing commercially feasible and pollution free.

What is claimed is:

1. A process for the recovery of metals of Groups I-B, IIB, IV-A, V-A,VI-A and VIII of the Periodic Table from their sulfides and mixedsulfides, and mixtures thereof, by electrolysis with the formation ofelemental sulfur and metal ions, which process comprises:

(a) providing an electrolyte in an electrolytic cell including at leastan anode and a cathode, the electrolyte comprising an acidic aqueoussolution of at least one chloride salt selected from the groupconsisting of chlorides of aluminum, chromium, copzinc was slurried in 2liters of electrolyte and subjected 55 P iron, malfgamse, nickel, Zinc,f rare ear h to 30 ampere hours of current under the conditionsindimetals, and mlXfllres thereof, he SOIHUOH havlng a cated with thefollowing results. concentration from about .5 N to saturation;

Test No 1 2 3 4 Electrolyte 3 M ZnCl 1.5 M ZnClr 3 M ZnCh 3 M ZnOlz.

Temperature 0.)- 75 75 75 75.

pH 0.8... o.&.. 0.3.. 3.5.

ACD (amps/IL) 120 120 120 120.

Amp-hrs/lb. Zn recovered 386 an 372 381.

Sulfur recovered (gms.) 13.2--- 16.8 12.7.-- 9.7.

Percent S as elemental S 89 83 71.

The tests illustrate that zinc chloride is as effective as (b) mixingwith the electrolyte a solid feed sulfide of an electrolyte as the otherchloride electrolytes of the the metal having an average particle sizesmaller invention. Test No. 4 was performed at a 3.5 pH which than about60 mesh US. Standard; is near the top of the critical pH range of 3.9and this (0) maintaining the temperature of the electrolyte test showsthe adverse efiect of low acidity on conversion media at about 50 C. toC., and the pH of of sulfide sulfur to elemental sulfur. 75 theelectrolyte media below about 3.9 while intro- 1 1 ducing electriccurernt into the electrolytic cell to provide an anode current densityabove about 12 amperes per square foot to dissociate the metal sulfideinto metal ions and elemental sulfur; and

(d) recovering metal from the electrolyte.

2. The process of claim 1 in which at least one chloride salt selectedfrom the group consisting of alkali metal chlorides and alkaline earthmetal chlorides is added to the electrolyte.

3. The process of claim 1 in which the metal is recovered from thesulfide and mixed sulfide in the presence of iron sulfides.

4. The process of claim 1 including the step of recovering the metalfrom solution in the electrolyte by electrodeposition on the cathode.

5. The process of claim 1 including the step of recovering elementalsulfur from the electrolyte.

6. The process of claim 1 in which the metal recovered is copper.

7. The process of claim 1 in which the metal recovered is lead.

8. The process of claim 1 in which the metal recovered is silver.

9. The process of claim 1 in which the metal recovered is zinc.

10. The process of claim 1 in which the metal recovered is antimony.

11. The process of claim 1 in which the metal recovered is arsenic.

12. The process of claim 1 in which the metal recovered is cadmium.

13. The process of claim 1 in which the metal recovered is selenium.

14. The process of claim 1 in which the metal recovered is nickel.

15. The process of claim 1 in which the metal recovered is cobalt.

16. The process of claim 1 in which the metal recovered is iron.

17. The process of claim 1 in which the metals are selected from thegroup consisting of antimony, arsenic, cadmium, copper, cobalt, iron,lead, nickel, selenium, silver and zinc.

18. The process of claim 1 in which the electrolyte is aluminumchloride.

19. The process of claim 1 in which the electrolyte is copper chloride.

20. The process of claim 1 in which the electrolyte is chromiumchloride.

21. The process of claim 1 in which the electrolyte is ferrous chloride.

22. The process of claim 1 in which the electrolyte is manganouschloride.

23. The process of claim 1 in which the electrolyte is nickelouschloride.

24. The process of claim 1 in which the electrolyte comprises at leastone rare earth metal chloride.

25. The process of claim 1 in which the electrolyte is zinc chloride.

26. The process of claim 25 in which the metal is zinc.

27. The process of claim 24 in which the metal is copper.

28. The process of claim, 23 in which the metal is copper.

29. The process of claim 22 in which the metal is copper.

30. The process of claim 31 in which the metal is copper.

31. The process of claim 21 in which the metal is selected from thegroup consisting of antimony, arsenic, cadmium, cobalt, copper, iron,lead, nickel, selenium, and

zinc.

32. The process of claim 20 in which the metal is copper.

33. The process of claim 19 in which the metal is copper. 34. Theprocess of claim 35 in which the metal is selected from the groupconsisting of lead, silver and 35. The process of claim 18 in which themetal is selected from the group consisting of silver, copper, iron,lead and zinc.

, 36. The process of claim 2 in which the alkali metal chloride issodium chloride.

37. A process for the recovery of metals of Groups I-B, II-B, IV-A, V-A,VI-A and VHI of the Periodic Table from their sulfides and mixedsulfides, and mixtures thereof, by electrolysis with the formation ofelemental sulfur and metal ions, which process comprises:

(a) providing an electrolyte in an electrolytic cell including at leastan anode and a cathode, the elect-rolyte comprising an acidic aqueoussolution of at least one soluble halide salt selected from the groupconsisting of soluble halide salts of aluminum, chromium, copper, iron,manganese, nickel, zinc, and rare earth metals, and mixtures thereof,the solution having a concentration from about .5 N to saturation;

(b) mixing with the electrolyte a solid feed sulfide of the metal havingan average particle size smaller than about 60 mesh U.S. Standard;

(c) maintaining the temperature of the electrolyte media at about 50 C.to C., and the pH of the electrolyte media below about 3.9 whileintroducing electric current into the electrolytic cell to provide ananode current density above about 12 amperes per square foot todissociate the metal sulfide into metal ions and elemental sulfur; and

(d) recovering metal from the electrolyte.

U.S. Cl. X.R. 204106, 107, 111, 113, 117, 118, 123, 293

